History

Manifestations of H1N1 influenza (swine flu) are similar to those of seasonal influenza. Patients present with symptoms of acute respiratory illness, including at least 2 of the following:

Fever

Cough

Sore throat

Body aches

Headache

Chills and fatigue

Diarrhea and vomiting (possible)

Persons with these symptoms should call their health care provider promptly. If an antiviral agent is warranted, it should ideally be initiated with 48 hours from the onset of symptoms (see Medication). The duration of illness is typically 4-6 days. The infectious period for a confirmed case is defined as 1 day prior to the onset of symptoms to 7 days after onset.

In children hospitalized for influenza, neurologic complications are common and sometimes life-threatening. In an effort to assess the extent and range of such complications in this population, Australian investigators in 6 tertiary pediatric referral centers carried out active hospital-based surveillance of 506 children younger than 15 years who had laboratory-confirmed pandemic influenza A (H1N1) 2009 infection (pH1N1'09).
[23] Of the 506, 49 (9.7%) had neurologic complications.

Further study findings were as follows:

Patients with neurologic complications tended to be slightly older than those without (median age, 4.8 years versus 3.7 years)

Of patients with neurologic complications, 55.1% had preexisting medical conditions and 42.8% had preexisting neurologic conditions

On presentation, only 36.7% had cough, fever, and coryza or runny nose; 38.7% had only 1 respiratory symptom or none at all

Neurologic complications, in descending order of frequency, included seizure (7.5%), encephalitis or encephalopathy (1.4%), confusion or disorientation (1.0%), loss of consciousness (1.0%), and paralysis or Guillain-Barré syndrome (0.4%)

Intensive care unit (ICU) admission was required in 30.6% of the patients, mechanical ventilation in 24.5%

Mean hospital stay was 6.5 days, mean ICU stay 4.4 days

Two (4.1%) of the 49 patients died

Specific treatment for influenza-related neurologic complications is generally unavailable. Consequently, early diagnosis of influenza, appropriate use of antiviral therapy, and universal influenza vaccination in children are vital. Influenza should be considered as a diagnosis in children with neurologic symptoms, even when few or even no respiratory symptoms are noted.

References

CDC. Interim Guidance for Clinicians on the Prevention and Treatment of Swine-Origin Influenza Virus Infection in Young Children. Centers for Disease Control and Prevention. Available at http://www.cdc.gov/swineflu/childrentreatment.htm. Accessed: April 30, 2009.

CDC. Interim Guidance on Specimen Collection and Processing for Patients with Suspected Swine Influenza A (H1N1) Virus Infection. Centers for Disease Control and Prevention. Available at http://www.cdc.gov/swineflu/specimencollection.htm. Accessed: April 28, 2009.

CDC. Interim Guidance on Antiviral Recommendations for Patients with Confirmed or Suspected Swine Influenza A (H1N1) Virus Infection and Close Contacts. Centers for Disease Control and Prevention. Available at http://www.cdc.gov/swineflu/recommendations.htm. Accessed: April 28, 2009.

CDC. Interim Guidance for Infection Control for Care of Patients with Confirmed or Suspected Swine Influenza A (H1N1) Virus Infection in a Healthcare Setting. Centers for Disease Control and Prevention. Available at http://www.cdc.gov/swineflu/guidelines_infection_control.htm. Accessed: April 29, 2009.

Phase 6 criteria: In addition to the criteria defined in Phase 5, the same virus has caused sustained community-level outbreaks in at least one other country in another WHO region. Courtesy of the WHO.